The present invention relates to an occipito-cervical osteosynthes is instrumentation and a hook intended to be part of this instrumentation.
It is known that in orthopaedic surgery on the cervical spine, when an instrumentation is required to realize an occipito-cervical arthrodesis, the surgeon generally uses an instrumentation composed of plates and screws. There has thus been put on the market an assembly having the general shape of a horseshoe constituted by two rods in one piece with a curved connection plate, the rods being knurled and disposed in the cervical part while the curved plate is in the occipital part. The hooking to the cervical vertebrae is achieved by thoracic and pediatric laminar hooks while the connection of the plate to the occiput is achieved by a plurality of screws.
This device has a drawback in that it cannot be shaped sufficiently to the anatomical configuration of the patient, above all in the cervical part. Indeed, it is difficult to adapt the distance between the two rods in the cervical part while achieving a suitable bending of the curved connecting plate.
Further, in orthopaedic surgery of the cervical segment, pathologies are encountered concerning the upper cervical vertebrae Atlas (C1) and Axis (C2). Among these there are essentially found degenerative pathology (cerviarthrosis) and tumoral traumatic pathology. When an instrumentation is used in the rear approach, this instrumentation comprises either rods or plates, their common purpous being to isolate the pathological segment by connecting the occiput to the subjacent healthy vertebrae. Thus there are known various instrumentation rods, frames and plates, in particular the Cotrel Dubousset rod, the Privat plate, the Roy Camille plate, etc. The means for connecting these different plates to the bone (occiput or vertebrae) comprise the following elements:
a) articular screws (inserted in the articular massives) and occipital screws, PA1 b) occipital screws and laminar hooks bearing against the vertebrae, PA1 c) metal wires constituting a bone lacing.
It is also known from the French patent application 92 01 913 (2 687 561) to construct an occipito-cervical device in which the two cervical rods are extended by curved plates which are themselves connected at their ends by a transverse connection plate. The assembly is fixed to the occiput by means of screws extending through openings in the connection plate so that a certain adjustment to the desired conformation is possible.
However, here again, the possibilities of an anatomical adaptation are in fact limited, notwithstanding the fact that this device provides a possibility of adjustment relative to the preceding device.
In order to fasten the rods of these instrumentations to the base of the occiput, there are in particular used hooks constituted by a body and a laminar portion which is adapted to enter the foramen opening at the base of the occiput against which the hook therefore bears. Now, the anatomy of the edge of the foramen in the regions where the hooks must bear is such that, in practice, in order to be in a position to conciliate both a correct orientation of the rod which extends through the body of the hook and a suitable bearing of the laminar portion of the latter on the base of the occiput, it is necessary to remove a piece of the occiput and therefore to damage it.